Traditionally, the Sovereign owns all unmarked mute swans on the River Thames. Under a Royal Charter of the fifteenth century, the Vintners' Company and the Dyers' Company, two Livery Companies of the City of London, are entitled to share in the Sovereign's ownership. The ceremony of Swan Upping occurs annually during the third week of July. During the ceremony, the Queen's, the Vintners', and the Dyers' Swan Uppers row up the river in skiffs. Swans caught by the Queen's Swan Uppers remain unmarked, those caught by the Dyers' are ringed on one leg, and those caught by the Vintners are ringed on both legs.